This invention relates generally to electromagnetic flowmeters, and more particularly to a flowmeter liner which is integrated with the flowmeter electrodes to define a monolithic conduit structure.
An electromagnetic flowmeter is adapted to measure the flow rates of those fluids which present difficult handling problems, such as corrosive acids, sewage slurries, detergents and the like. In a flowmeter of this type, the liquid whose flow rate is to be measured is conducted through a flow tube provided with a pair of diametrically-opposed electrodes, a magnetic field perpendicular to the longitudinal axis of the tube being established by a pair of diametrically-opposed electromagnets. When the flowing liquid intersects this field, a voltage is induced therein which is transferred to the electrodes. The voltage, which is proportional to the average velocity of the liquid and hence to its average volumetric rate, is then amplified and processed to actuate a recorder or indicator, or to supply an input variable to a process control system.
In a flowmeter of this type, such as that disclosed in the Schmoock et al. U.S. Pat. No. 3,839,912 (1974), it is common practice to install an electrically-insulating liner on the inner surface of the metal flow tube. The outer metal flow tube provides a structure capable of withstanding the operating pressures to which the meter is subjected, whereas the inner liner functions as the flow conduit.
Often employed as insulating liners are liners molded of fluorocarbon materials such as PTFE, PFA and FEP. Because fluorocarbons are non-reactive with virtually all corrosive fluids, they have desirable liner properties. But since the meter electrodes which conventionally are of metal must have their faces exposed to the liquid flowing through the conduit, the liner is indented to accommodate the metal electrodes, the geometry of the indentation conforming to the periphery of the electrodes.
While it is also the practice to cement the electrodes to the liner, because the materials thereof are dissimilar, it is difficult to produce a seal therebetween capable of withstanding the pressures encountered in flowmeters and of resisting the corrosive and abrasive actions of the fluids being metered. As a consequence, leaks are often developed at the interface of the electrodes and the liner. These leaks create serious operating problems, and in some instance may render the meter inoperative.